Servovalve construction



May 27, 1969 J. L. COAKLEY ET AL SERVOVALVE CONSTRUCTION Original FiledMarch 1, 1966 Sheet of 5 May 27, 1969 J. L. COAKLEY ET Al. 3,447,111

SERVOVALVE CONSTRUCTION Original Filed March l. 1966 Sheet of 3 yINVENTORS mi? 1% May-27, 1969 J.| .c:oAK| EY ETAL l 3,447,111

sERvovALvE CONSTRUCTION Orinal Filed March l. 1966 sheet 5 @f3 WMMArm/@Mix United States Patent O U.S. Cl. 335-230 7 Claims ABSTRACT OFTHE DISCLOSURE A torque motor having its armature lmounted to a torsionmember which is fixed to the armature at one point and fixed to a baseat a second point. The torsion member is twisted axially by armaturerotation. The armature operates a shaft or driver which is connected, ata position spaced from the connection of the armature to the torsionmember, to transversely swingable output movement means. The outputmovement means are angularly disposed with respect to the shaft and areconnected between the base and the shaft, and include a flexible portionbetween the connections to the base and the shaft.

This application is a division of my copending application Ser. No.530,916, filed Mar. l, 1966.

This invention relates to servomechanisms and more particularly tolforce feedback operated servovalves.

Servovalves of the general type to which this invention relates areoperated by a torque motor and include two force amplification stages.Application of an electrical input control signal to an electromagnetcoil in the torque motor causes an unbalanced flux distribution in theair gaps around the motor armature, causing a torque to act on thearmature. The armature rotates in response to this torque, againstspring means which bias the armature to its centered or null position.Movement of the armature shifts a jet of fluid issuing from a jet tubefrom a null position in which it is centered between two receiver ports,to a new position in which the jet impinges unequally on the two ports.This deflection of the jet establishes a differential pressure betweenthe receiver ports lwhich is proportioned to the input current. Thefluid employed in conjunction with the jet tube may, of course, beeither hydraulic or pneumatic fluid. ln the description to follow, it isassumed that hydraulic fluid is utilized.

lThe pressures in the receiver ports are fed to the second stage of theservovalve, which is a spool valve hydraulic force amplifier. Thedifferential pressure input from the first stage is reflected on opposedsurfaces of a main spool or piston in the second stage, shifting thespool and establishing communication between various ports. Flow throughthese ports in the second stage varies with spool position. Spoolmovement in response to the differenial pressure continues until afeedback spring member, through `which the spool and jet tube arecoupled, becomes sufficiently stressed that it returns the jet to thenull position, thereby removing the pressure differential on the spool.When this has occurred the spool thereafter remains in thatposition,controlling flow through the second stage at a rate and directioncorresponding to the magnitude and polarity of the electrical inputsignal to the torque motor.

From an economic standpoint as well as from a performance standpoint,the servovalves of the prior art have not been entirely satisfactory.The dissatisfaction can be traced to a number of structural featureswhich, because of their design, have introduced complexities into themanufacture and assembly of the various component parts constituting thevalve. These complexities, in addition to increasing the costs ofmanufacture and assembly, have inherently limited the performance of theearlier valves.

For example, in one type of prior art servovalve the spring means usedto bias the torque motor armature and jet tube to their balanced,central or null positions has included a tubular element which surroundsthe jet tube and which functions in bending as a spring when thearmature and jet tube are moved from their null positions.

In such valves, the spring means bends as the armature rotates inresponse to a signal. The extent to which the spring means bends isproportional to the total spring constant, which in turn is a functionof spring shape and thickness. Since predictable and reliable operationrequires close control of the spring constant, it has been foundnecessary in practice to machine these items with precision in order toaccurately regulate their characteristic, and, hence, their springrates. This need for precision machining has obviously added to the costof such servovalves.

It has been an objective of this invention to provide an improvedservovalve torque motor having an armature supporting and biasing springwhich is more efiicient of less critical manufacture, and which also ismore economical than those which previous torque motors have used.

A 'further disadvantage of previous valves of the general type describedis that they have not readily lent themselves to room temperatureassembly procedures such as swaging, crimping, etc. Soldering or brazinghas usually been required to make the critical connections, whichinvariably requires more skill, is costlier, and tends to producewarpage which may adversely affect valve operation unless compensated.

It has been a further object of this invention to provide a servovalveconstruction rwhich eliminates the need for soldered or brazedconnections at critical points, thereby eliminating warpage andmisalignment which might otherwise be caused by heating of componentparts during assembly.

Moreover, the prior art servovalves have often been difficult toassemble and align or adjust for maximum operating eficiency andperformance. Once assembled, they have been difficult to disassemble forcleaning, repair, and inspection purposes.

It has been an additional object of this invention to provide aservovalve which can be assembled and disassembled relatively easily,and in which the first and second stages are separate subassemblies.

It has been another object of this invention to provide interlockingpole piece mounting means for a servovalve which permit accurate air gapdimensioning during assembly and protect against pole piece positionalshifts while in use.

In a preferred embodiment of the invention, the torque motor armaturehas a pair of arms or wings on either side of a transversely extendinghollow central body. An elongated armature restoring element in the formof a thin walled tube extends through the interior of the hollow centralbody of the armature. This tube is connected to and supports thearmature only at a point forward of the wings, and is connected to asupporting base only at a point on the rear side of the wings. A shaftor driver also extends through the armature, internally of the armaturerestoring tube, and is connected to the armature and tube only at thefront end thereof. Electromagnet coils are disposed on opposite sides ofthe armature and when energized are operative to turn the armature aboutthe common axis of the shaft and tube, thereby rotating the shaft. Theshaft or driver moves an elongated flexible jet tube which passesperpendicularly through an enlarged aperture in the rear portion of thedriver. The jet tube is secured at its uid inlet end to the body abovethe driver and is connected to the driver through an elongated tubewhich surrounds the jet tube and which is clamped to the jet tubeadjacent the fluid outlet end or nozzle thereof.

Use of the thinewalled tube described in this construction provides anumber of advantages: a single length of precision tubing serves jointlyas the support means for the armature, as a torsion spring biasing thearmature to null position, and as an isolation element for preventingoperating uid within the hydraulic portion of the valve from reachingthe inside of the electrical portion of the torque motor. In addition,the configuration of the hollow tube herein provided permits it to beconnected to the armature and supporting base by swaging techniques,thus avoiding the usual disadvantages of machining and warping due tosoldering or brazing during assembly.

In the torque motor, a pair of,opposed, nonlnagnetic membersmechanically engage reference surfaces on the pole pieces of theelectromagnetic coils and provide spacing means for establishing theproper air gap dimensions during assembly.

These and other objects and advantages of the present invention will bemore readily apparent from a consideration of the following detaileddescription of the drawings illustrating a preferred embodiment of theinvention.

In the drawings:

FIGURE 1 is a vertical section of a preferred embodiment of theservovalve of this invention, and is taken along the axis of the torquemotor.

FIGURE 2 is a longitudinal section taken along line 2-2 of FIGURE 1, andalso illustrates a typical hydraulic system including the servovalve.

FIGURE 3 is an enlarged vertical axial section of the rst stage of thevalve, showing the details of the torque tube, armature, hydraulic jettube and receiver, and the force feedback spring assembly.

FIGURE 4 is a section taken along line 4-4 of FIG- URE 3.

FIGURE 5 is a partially exploded perspective view of the torque motorassembly.

FIGURE 6 is an enlarged view in perspective of the armature.

FIGURE 7 is a side elevation of the assembled torque motor.

FIGURE 8 is an enlarged view in section of a portio of the jet tube andreceiver.

The servovalve of this invention includes three princip-al sections,namely, a torque motor 1, a first force lamplifying stage 2, and asecond force amplifying stage 3. As best shown in FIGURES l and 2, in apreferred embodiment, the torque motor 1 and first amplifying stage 2are supported by a common base or frame member 4. Base 4 is nonmagnetic,and is mounted on a body 5, the body 5 also serving as a casing for thesecond section 3 of the servovalve. A housing 6 mounted on ahorizontally extending ange 7 of the body 5 encloses motor 1 andamplifier 2.

The torque motor 1, as shown more particularly in FIGURES 5-7, includesa permanent magnet 8 having an upper north pole 9 and a lower south pole10. Magnet 8 may be an Alnico permanent magnet. Sandwiched betweenmagnet 8 and base 4 are opposed ferromagnetic upper and lower C-shapedpole pieces 11 and 12, respectively. The opposed planar end surfaces 13,14 and 15, 16 of pole pieces 11 and 12, respectively, are spaced,forming air gaps 17 and 18, respectively (see FIGURE 2). The permanentmagnet 8 functions to establish a unidirectional magnetic flux in eachof the air gaps 17, 18.

Also sandwiched between magnet 8 and base 4 are a pair of nonmagneticspacer members 19 and 201. Since members 19 and 20 are similar, only theleft member 19 will be described. Member 19 is C-shaped, as viewed fromabove, and includes opposed internal pole piece engaging surfaces 21, 22separated by pole piece end-engaging surface 23. Surface 22 is generallyplanar for engaging the back surfaces (adjacent base 4) of the polepieces 11 and 12 to align them in its plane. Pole piece-end-engagingsurface 23 is provided with a horizontal slot 25, and from this slothorizontal grooves 24 extend across the inner side faces of the spacerto permit the assembly to be placed over the armature. The surface 23abuts the ends of pole pieces 11 and 12, establishing alignment in itsplane. The angulated internal surfaces 21, 21 (see FIGURE 5 engage the*opposed beveled corner surfaces 26, 26 of the pole pieces 11, 12 andjointly function to locate and accurately space pole piece end surfaces13, 14, thereby dimensioning air gap 17. Thus, when spacer 19 is snuglytted over the left ends of the pole pieces 11 and 12, pole piecesurfaces 13 and 14 are horizontally and vertically aligned by surfaces22 and 23, as well as spaced apart to form an air gap 17 by angulatedsurfaces 21, 21. Those skilled in the art will recognize the criticalityof accurate air gap dimensioning.

A forwardly extending, vertical flange 27 is formed on the roundedexternal surface 28 of each spacing member. Flange 27 is provided with aflat shoulder surface 29, best shown on the spacing member 20 in FIGURE5, and engages and seats in the internal end surface 30 of the magnet 8,thereby preventing movement of the spacing member relative to polepieces 11, 12 when the motor 1 is assembled.

The motor 1 also includes a pair of coils 31, 32 through the opencenters of which extend the at wings 33, 34, respectively, of anarmature 35 described in detail hereinafter. In the assembled torquemotor 1, the coils 31, 32 are mounted by and between the opposed concavemagnet surface 30 and concave base surface 30a, pole pieces 11, 12, andspacing members 19, 20. The coil leads 36 pass through slots 37 in thespacing members 19, 20 for connection to a suitable electrical signalinput means (not shown) which may be conventional.

The various parts of the torque rnotor assembly are held in operativerelation by two screws 38 and a plate 39. The screws 38 passsuccessively through plate apertures 40, magnet aperture 41, grooves 42in pole pieces 11, 12, and thence into tapped holes 43 in base 4. Asscrews 38 are tightened, magnet 8 and base 4 are drawn together,gripping the pole pieces 11, 12 and holding the spacing members 19, 20between them. The spaces between members 19, 20 and faces 30, 30a arefilled with an epoxy which provides a positive interlock in the torquemotor.

The operation of the torque motor 1 follows principles which are Wellknown and need not be discussed in detail. It is sufficient for thepurposes of understanding the various features of this invention toappreciate merely that a differential current applied to coils 31, 32will result in a magnetic torque being applied to ferromagnetic armature35, rotating it about its axis 44. Armature 35 rotates -under the forceof the applied torque to an angular position Within air gaps 17, 18where the applied torque equals the armature restoring torque producedby means to be described. The direction and magnitude of the appliedtorque is dependent upon the level and polarity of the differentialcurrent owing in the coils 31, 32. For a detailed discussion of theoperation of torque motors, reference may be had to U.S. Patent2,891,181, to Raymond D. Atchley, issued June 16, 1959, and entitled,Torque Motor.

The armature 35 of motor 1 is generally T-shaped as viewed in plan, andincludes a central tubular portion 50 provided with oppositely extendingflat wings 33, 34 of equal length (see FIGURE 6). The dimensioning ofwings 33, 34 is such that they extend into air gaps 17, 18 respectively.Clearance is provided between the wings 33, 34 and the pole piece endsurfaces 13, 14 and 15, 16 respectively, permitting the armature 3S torotate about its axis 44 in response to the application of an electricalsignal to the windings 31, 32. The extent of armature rotation isselectively limited by adjusting screws 51, 51 threaded into tappedholes in upper pole piece 11 (see FIGURE 2).

The forward extremity of central tubular portion 50 of armature 35 has areduced internal diameter resulting in a stepped-diameter bore having asmall diameter bore section 52 and a large diameter bore section 53separated by an internal shoulder. Positioned Within the bore sections52, 53 is a non-magnetic stepped diameter armaturesupporting torque andisolation tube 54. The torque tube 54 is secured at its reduced diameterfront end portion 55 to the end 57 of the armature tubular portion 50,and at its other end 56 to the base 4. The portion of tube 54intermediate ends 55 and 56 is coextensive lengthwise with bore section53 of central armature portion 50, but is of reduced diameter and doesnot contact the armature.

The end 55 of torque tube 54 fits snugly within bore section 52 of thecentral armature portion 50 and is sec-ured in place by an internallytapered swaging ferrule 60 which is pressed over the externally taperedarmature end 57. The complementary tapers of armature end 57 and ferrule60 securely lock the armature 35 and torque tube 54 to the end of acoaxial driver 65, providing a solderless connection therebetween.

The tube 54 at its inner end 56 is flared and fits snugly into a taperedbore 61 in base 4. An externally tapered swaging ferrule 62 pressedwithin flared end 56 of torque tube 54 secures the torque tube to base4. The complementary tapers of swaging ferrule 62 and base bore 61 lockthe flared end 56 of torque tube 54, thereby providing a solderlessconnection between the base 4 and the torque tube 54.

Thus, armature 35 is supported within motor 1, with its wings 33, 34centrally positoned within air gaps 17, 18 and -biased against rotationabout its axis 44 by torque tube 54, the latter being connected at itsouter end 55 to the front end of the armature and at its inner end,beyond the opposite end of the armature, to base 4 via ferrules 60 and62, respectively.

The relation of the torque tube 54 and armature 35, as herein described,wherein the tube passes axially through the armature and is connected atits outer end to the armature enables a relatively long torque tube 54to be employed as the spring element in the torque motor 1. With a longtorque tube 54 in contrast to a short one, there is less angularrotation of the tube per unit length for a given armature rotation.

To transmit the torque output of motor 1 to the first amplifying stage2, a deflection or coupling means is provided. The coupling meansincludes a non-magnetic driver 65 which passes axially through torquetube 54. As previously mentioned, the outer end of driver 65 is securedto the armature 35 andtorque tube 54 by swaging ferrule 60. At its otheror inner end driver 65 is secured through `an element 66 having anopening extending therethrough at right angles to the driver, to an armor yoke 67 for movement therewith. Arm 67 has a right angle bendintermediate its ends, thereby forming an L-shape, and its lower portionthus projects forwardly beneath element 66 and .parallel to driver 65.The connection between the vertical leg 73 of arm 67 and element 66 isby a screw 68 which passes through an oversized hole 69 in leg 73 andwhich is threaded into a tapped hole 70 in element 66'. Radial teeth 71formed on the element face (see FIGURE 4) engage the forward surface 72of vertical leg 73 to prevent relative angular movement between collar66 and arm 67 when screw 68 is tightened.

The lower or forwardly extending leg 74 of arm 67 is provided with twoholes 75 and 76. A tube 77 is secured in hole 76 by suitable means.Soldering or brazing may be employed here since warpage is not criticalat this point. The lower end of tube 77, including the reduceddiameterlower end portion thereof, has circumferentiallyspaced longitudinalslots 78 therein. The slots 78 enable the reduced-diameter portion oftube 77 to securely embrace the periphery of a vertically disposedflexible jet tube 85. This tube extends through and is gripped by thelower end portion of tube 77 under the action of a press fitted ring 80which clamps the slotted, reduced-diameter end portion of tube 77 to jettube 85.

In the first amplifying stage 2, jet tube extends through tube 77, hole76, and element 66 and is secured at its upper end only to base 4 -by aconical-ended retainer plug 86 and screw 84. Plug 86 and screw 84cooperate with the sloping walls 87 of a threaded hole 88 to securelylock the flared end 89 of jet tube 85 relative to base 4 when screw 84is tightened. At its lower end, jet tube 85 is fitted internally with aprojector jet 90 having an outlet nozzle and which is secured in placeby a crimp 91.

The first amplifying stage 2 also includes a receiver 92. Receiver 92 isa plug having a pair of fluid passages 93, 94 (see FIGURE 8) Awhich meetover a central knife edge 95. Passages 93, 94 communicate with passages96, 97, respectively, formed in a receiver supporting member 98. Thepassages 96, 97 in turn communicate with passages 99, 100 (see FIGURE 2)which constitute the inputs to the second amplifying stage 3.

The receiver supporting member 98 is connected to base 4 by means notshown and, when the servovalve is assembled, is positioned within acavity 101 in body 5, seating and sealing on surface 102 thereof. Apassage 103 is formed in member 98 which connects the upper end of jettube 85 to a source of pressure fluid via passage 104 in plug 86,passage 105 in base 4, passage 106 in body 5, filter 107, and inlet port108 in body 5.

In operation, when an electrical signal is applied to the torque motor1, armature 25 initially rotates from a centered position to a pointwhere the restoring force on the armature 35 equals the magnetic torqueproduced by the electrical input. These restoring forces arise fromdeflection of the torque tube 54, jet tube 85 and a feedback spring tobe described. The armature rotation is transmitted to the jet tube 85via driver 65, element 66, arm 67, and tube 77, bending or defiectingjet tube 85 from a centered position directly over knife edge 95 of thereceiver. As the jet tube 85 is deflected lfrom the centered, nullposition shown in FIGURE 8, it directs a greater proportion of the fluidissuing from its nozzle 90 to one or the other of the receiver passages93, 94. The pressure in that receiver passage toward which the nozzle 90is deflected will increase while the .pressure in the other passage Willdecrease. Excess pilot flow from jet tube 85 -which is not accepted byeither receiver passage flows to a fluid reservoir. Thus a differentialbetween the pressures in passages 93 and 94 is developed. Thisdifferential constitutes the input to the second amplifying stage. Aslight rotation of armature 35 produces a relatively large displacementof jet tube 85 and a relatively large pressure differential developsbetween passages 93 and 94. This pressure differential is capable ofdeveloping much larger forces than could be developed by the armaturealone. Hence, force multiplication is produced by the first amplifyingstage.

The second amplifying stage 3 includes a main spool valve having a spoolor piston 110 slidable in a bore 111 of a sleeve 112 (see FIGURE 2).Spool 110 has a series of axially spaced peripheral grooves G1, G2, andG3. Sleeve 112 is fitted into a bore 113 in the body 5 and it isprovided with a plurality of port means P1, P2, P3, P4, and P5 whichcommunicate with bore 111 at axially spaced positions, and whichcooperate with spool grooves G1G2 to direct the flow of fluid throughthe main valve. Ports P1-P5 can be interconnected in various ways by theselective positioning of spool 110 relative to sleeve 112. For example,if the spool valve is to control or meter the flow of fluid a variablespeed reversible motor M, motor ports M1 and M2 may be connected toports P2 and P4, respectively. The .pump outlet port is connected toboth ports P1 and P5, and port P3 is connected to a tank T. In such asystem, when spool 110k is moved to the right in sleeve 112, the motor Mis driven in one direction by fluid 'from pump P which takes thefollowing path: port P1, groove G1, port P2, motor port M1, motor M,motor port M2, port P1, groove G2, port P3, to tank T. If spool 110 ismoved to the left, motor M is driven in the opposite direction by fluidfrom pump P taking the path through port P5, groove G3, port P4, `motorport M2, motor M, motor port M1, port P2, groove G2, port P3, to tank T.The speed at which motor M is driven depends, of course, on the ow ratethrough motor M, which in turn depends on the extent to which spool 110is displaced from the centered position wherein no flow occurs.

The port P3 in sleeve 112 also communicates with the region surroundingprojector jet 90, thereby providing a path to tank T for excess jetstream fluid not entering either of the two receiver ports 93, 94.

The means for selectively moving spool 110 includes pressure chambers115 and 116 in bore 111, pressure in which acts upon the opposite endsurfaces of spool 110. Chambers 115 and 116 communicate with passages99, 96, 93 and 100, 97, 94 respectively, and reflect the differentialestablished by the first stage. Adjustable stops 117 and 118 are sealedto bore 111 and can be positioned axially therein to limit the movementof spool 110 by plugs 119 and 120 respectively lwhich are threaded intobody 5.

In operation, the input to the second amplifier stage 3, that is, thepressure differential between passages 93, 94, produces a differentialor net axial force on spool 110. The direction which this differentialforce moves spool 110 depends upon the polarity of the electrical signalinput to the motor 1. Thus, fluid flows to motor M, in the selecteddirection.

Since the electrical signal is supplied for as long as it is desired todrive motor M, which usually will be much longer than it takes spool 110to shift an amount corresponding to the flow rate and motor speeddesired, force feedback means are provided. This force feedback meansincludes a feedback spring 125 which is connected at its upper end 126to horizontal leg 74 of arm 67. The connection is effected by securingend 126 in hole 75. The other end 127 of spring 125 has a ball 128attached thereto. Ball 128 ts accurately and without play in a crossbore 129 in spool 110 forming a cam connection between the spool and thefeedback spring.

Spool 110 will move in sleeve 112 as long as there is a pressuredifferential between chambers 115 and 116. Since this pressuredifferential is caused by the unequal impingement of fluid on receivers93, 94 due to the deflection of jet tube 85, the force on spool 110 willremain as long as the jet pipe 85 is deflected. However, spring 125 isresponsive to the position of spool 110, and supplies a feedback forceto driver 65 which returns jet tube 85 to null position and therebyremoves any net force on the spool 110 when the spool has been shiftedan amount corresponding to the magnitude of the input signal.

By way of example, referring to FIGURE 2, a counterclockwise jet tuberotation will produce an unbalanced force in chamber 116 which shiftsspool 110 to the left. As spool 110` moves to the left, it rotates thefeedback spring 125 clockwise. This clockwise motion is transmitted toarm 67, which in turn transmits it to the arma-V ture and tends to turnthe jet tube clockwise to the null position. The spool position at whichfeedback spring 125 returns jet tube 85 to the null position correspondsto a unique and discrete input current level. Hence the servovalve willregulate the speed of motor M in accordance with the input signal. Thespool 110 will remain in this position until the electrical signal isagain varied.

It will be apparent from the symmetry of the valve that oppositely poledelectrical input signals rotate the armature 35 and torque tube in theopposite direction, causing the spool to move toward the other side ofits center or neutral position.

From theforegoing it will be apparent that the interrelation of thearmature, torque tube, driver, arm, jet

tube, and force feedback spring provides an assembly which isexceedingly compact in relation to the high gain which can be attained.The torsion spring length is relatively large in proportion to the smallsize of the assembly, as shown in FIGURE 3. Moreover, the arrangement ofthe first stage elements wherein the jet pipe projects through thedriver and is engaged by the outer tube 77 only adjacent its lower end,provides a relatively long lever anm in compact form. Assembly of thevalve is facilitated since the entire rst stage subassembly forms anintegral unit with torque motor 1 which can be fitted as a unit to thesecond stage 3.

While we have described a preferred form of this invention, it will beunderstood that it is susceptible of various modifications andadaptations within the scope of the following claims.

What is claimed is:

1. A torque motor comprising:

a base,

magnet means mounted to said base, said magnet means having spaced polesdefining an air gap between them,

coil means,

an armature having an axis of rotation, said armature including aportion extending into said air gap for magnetic interaction with fluxin said gap,

a torsion member connected between said armature and said base ataxially spaced positions for torsionally constraining the rotation ofsaid armature about said axis, said armature being supported only bysaid torsion member to be rotated about the axis of said member inresponse to the application of an electric signal to said coil,

a shaft coupled to said armature for rotation therewith,

said shaft providing a rotational movement correlated with the magnitudeof said electric signal,

and transversely swingable output movement means angularly disposed withrespect to said shaft, said output movement means being connectedbetween said base and a position on said shaft spaced from theconnection of said torsion member to said armature, said output movementmeans including a flexible portion between the connections to said baseand said shaft.

2. The torque motor of claim 1 wherein said magnet means comprises apermanent magnet and two separate pole pieces in magnetic circuitrelation therewith, said pole pieces presenting opposed referencesurfaces, a reference surface being formed adjacent each air gap andextending angularly with respect thereto:

and a nonmagnetic lmember having angulated opposed spaced surface meansextending between and engaging said reference surfaces of said polepieces, said surface means disposed to oppositely align said pole piecesand to establish a predesigned minimum air gap width. j

3. The torque motor of claim 2 wherein said motor includes an air gap oneach side of said axis, said armature is symmetrical about said axis andincludes opposed portions extending into said air gaps, there also beinga pair of said nonmagnetic members:

said pole pieces and nonmagnetic members being clamped in sandwichrelation between said permanent magnet and said base.

4. The torque motor of claim 1 wherein said armature includes a flatwing on each side of an axially disposed hollow central portion, theaxial dimension of said central portion exceeding the axial dimension ofsaid wings, and further wherein said torsion spring extends through saidhollow portion of said armature and is connected to said armature onlyat one end of said central portion at a point spaced axially from saidwings.

5. The torque motor of claim 1 wherein said output movement meansprojects freely through a diametrical opening in said shaft and isconnected to said shaft at a point thereon spaced axially from saidopening.

6. The torque motor of claim 5 wherein said output movement means has afree outer end on one side of said dialmetrical opening and is connectedto said shaft by an arm between said outer end and said point on saidshaft.

7. A torque motor comprising:

a base having a bore therethrough,

a tube having one end positioned and sealed in said bore,

an armature disposed coaxially around said tube and rigidly connected tosaid tube at a second end thereof, said tube between its ends passingfreely through an axial opening provided in said armature, magneticmeans for exerting rotational force on said armature, said meansdisposed to urge said Iarmature to rotate about the axis of said tube,said tube torsionally resisting such rotation of said armature, a shaftcoupled to said armature for rotation therewith,

said shaft extending axially through the center of said tube and havinga portion projecting beyond said tube through said bore,

and elongated exible output movement means connected at one end to saidbase and extending angularly with respect to the axis of said shaft,said output movement means also being connected to the p0rtion of saidshaft which projects beyond said tube.

References Cited UNITED STATES PATENTS 2,905,871 9/1959 Martn 310-36 XR3,076,920 2/1963 Gordon et al. 335--230 3,214,646 10/1965 Duif 31036 XRGEORGE HARRIS, Primary Examiner.

U.S. C1. X.R. 310-36

